None
The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.
This invention relates to laser propelled vehicles, particularly launching such vehicles or craft with a laser beam.
The fundamental problem facing our nation""s ability to conduct routine space operations is the high cost now associated with conducting launch operations with conventional chemical rockets. Current information shows that it costs between $2,500 and $12,000 a pound to reach low-earth orbit. Chemical rockets typically carry their working fluid and energy source (propellants) on board. This results in a payload fraction (satellite weight/total rocket weight) of only a few percent. Rocket based combined cycle concepts employing momentum exchange with the atmosphere during a portion of the ascent and pure rocket propulsion as it enters space, can reduce costs by perhaps a factor of two and improve the payload fraction slightly. No other near term chemically-fueled launch vehicle prospects are in view that can create a significant reduction in space launch cost and payload.
Laser propelled lightweight vehicles, e.g. 20-60 grams have been tried and flown for short distances. See for example xe2x80x9cGround and Flight tests of a Laser Propelled Vehiclexe2x80x9d by L.N. Myrabo et al. Jan. 12-15, 1998, AIAA 98-1001 and a subsequent paper entitled xe2x80x9cFlight and Ground Tests of a Laser-Boosted Vehiclexe2x80x9d by F. B. Mead, Jr. et al. Jul. 13-15, 1998, AIAA 98-3735, which papers are incorporated herein by reference.
However, such systems have succeeded in vertical laser propulsion of a vehicle for only short vertical distances, e.g., up to 28 meters and there is need and market for a laser propulsion system that surpasses such altitudes.
There has now been discovered a laser propulsion system that can boost such vehicles considerably higher, e.g., up to 100 meters or more, toward suborbital or orbital flights including, launch-to-orbit of satellites and other payloads at greatly reduced costs.
Broadly the present invention provides a laser propelled vehicle or craft comprising,
a) forebody or nose,
b) a tapering afterbody optic and
c) an annular shroud mounted around and between the extremities of the forebody and the afterbody, which shroud extends aft and defines an annular space around a portion of the afterbody and
d) means to direct a laser beam toward said afterbody and thence to the annular shroud, to heat and pressurize the air in the annular space to an expanding plasma to propel the craft; the afterbody and shroud being so shaped as to self center or remain in the laser beam as the craft is propelled thereby.
The above embodiment is employed in the atmosphere up to an altitude of, e.g., 30 km and is designated herein as the air-breathing embodiment of the invention.
In a second (or hybrid) embodiment of the invention, the lasercraft of the invention can carry a propellant therein so that after launch it can transition from air breathing to rocket mode, as discussed below. The above lasercraft is initially an air breathing laser propulsion system. However air-breathing engines can only be used within the atmosphere and such craft going into space must, in reality, carry some additional propellant on board for operation in the vacuum of space. Being able to operate well, either with just an air based propellant and also with an onboard propellant, is the definition of a xe2x80x9cdual-modexe2x80x9d engine. In the case of launching the lasercraft of the invention into orbit, propellant is carried on board for use above, e.g., at an altitude of up to 30 km (18.6 mi or roughly 100,000 ft) and at a velocity of up to Mach 5. Thus for an actual space mission, the lasercraft would carry about half its weight in propellant.
In a third embodiment, the lasercraft of the invention carries a propellant on board, which is heated to ablation at launch and thereafter, by a laser beam to generate thrust and accordingly operates at all times as a rocket engine, through the atmosphere in a suborbital path or into space in an orbital path, as desired.
All three of the above embodiments can fly suborbital paths and in the case of embodiments two and three hereof, fly as well, in orbital flight paths per the invention.
Definitions:
By xe2x80x9cair plasmaxe2x80x9d as used herein, is meant air heated sufficiently high by the inverse Bremsstrahlung Process to provide dissociated and ionized particles, including those of oxygen and nitrogen, which subsequently produce a high pressure burst of thrust between shroud and afterbody, created by laser supported detonation (LSD) and/or combustion(LSC) waves. Between such laser pulses or the propulsion bursts, new air rushes into the annular space to await the next laser pulse.
By xe2x80x9claser craftxe2x80x9d, as used herein, is included the alternate designation of xe2x80x9claser lightcraftxe2x80x9d.